The therapeutic activity of the narcissus residual alkaloid A-2 against Rauscher leukemia has been compared with 10 standard anticancer drugs, and synergistic or additive combination pairs have been selected using the viral leukemia and two transplantable tumor systems (Ehrlich and MCDV-12). An increased beneficial effect has been demonstrated by a combination of the alkylating and DNA-binding agents, and the alkaloid against the three malignant tumors, while a beneficial effect by combining the alkaloid and the antimetabolites, (either 6-MP or 5-azacytidine), was seen only against the viral leukemia. The alkaloid has no suppressive activity against cellular immunity as tested by PHA reactivity and allogeneic tumor rejection systems. The residual alkaloid A-3, chromatographically purified grade, has been identified as pretazettine.